The present invention relates generally to a system and a method for controlling a pump in a recirculating hot water system and, more particularly, to a system for controlling a pump in accordance with a measured demand for hot water.
Any system for providing hot water in a building must be capable of providing sufficient hot water to supply the needs of the building's occupants. Traditionally, this has been accomplished using a recirculation pump to circulate the heated water from a hot water heater to occupants and an internal thermostatic control, or “aquastat”, to control the temperature of a hot water heater or boiler. The recirculation pumps are typically operated at a constant or fixed speed. During non-peak periods, the practice of operating the recirculation pump at constant or fixed speed results in both heat loss in the hot water system and electrical energy loss in the recirculation pump. A system and method for controlling a hot water heater to reduce heat loss during periods of non-use is discussed in U.S. Pat. No. 5,626,287 to Krause et al., the entire content of which is expressly incorporated herein by reference.
The electrical energy loss for fixed speed operation of a recirculation pump during non-peak periods can be substantial. Further, such operation is particularly inefficient in large recirculating hot water systems featuring pumps capable of circulating significant volumes of water. In a number of hot water systems, the recirculation pumps are oversized to meet maximum demand requirements for the heated water. Such oversized pumps consume even more electrical and thermal energy than the conventional recirculation pumps.